Models Of QOS

Quality of Service Models

In this post, we will see Models of QOS.A QOS model, also called a level of service, describes a set of end-to-end QOS capabilities. End-to-end QOS is the ability of the network to deliver service required by specific network traffic from one end of the network to another.

Cisco IOS QOS software supports three types of service models: best effort, integrated, and differentiated services.

This section describes these service models:

•          Best-Effort Service
•          Integrated Service
•          Differentiated Service

The features in Cisco IOS QOS software address the requirements for these service models.

Best-Effort Service

Best effort is a single service model in which an application sends data whenever it must, in any quantity, and without requesting permission or first informing the network. For best-effort service, the network delivers data if it can, without any assurance of reliability, delay bounds, or throughput.

The Cisco IOS QOS feature that implements best-effort service is first-in, first-out (FIFO) queuing. Best-effort service is suitable for a wide range of networked applications such as FTP, Exchange,etc.

Integrated Service

Integrated service is a multiple service model that can accommodate multiple QOS requirements. In this model the application requests a specific kind of service from the network before sending data. The request is made by explicit signalling; the application informs the network of its traffic profile and requests a particular kind of service that can encompass its bandwidth and delay requirements. The application is expected to send data only after it gets a confirmation from the network. It is also expected to send data that lies within its described traffic profile.

The network performs admission control, based on information from the application and available network resources. It also commits to meeting the QoS requirements of the application as long as the traffic remains within the profile specifications. The network fulfills its commitment by maintaining per-flow state and then performing packet classification, policing, and intelligent queuing based on that state.

Differentiated Service

Differentiated service is a multiple service model that can satisfy differing QOS requirements. However, unlike the integrated service model, an application using differentiated service does not explicitly signal the router before sending data.

For differentiated service, the network tries to deliver a particular kind of service based on the QOS specified by each packet.

This specification can occur in different ways, for example, using the IP Precedence bit settings in IP packets or source and destination addresses.

These features that support the differentiated service model:

·         Committed access rate (CAR), which performs packet classification through IP Precedence and QoS group settings. CAR performs metering and policing of traffic, providing bandwidth management.

·         Intelligent queuing schemes such as WRED and WFQ and their equivalent features on the Versatile Interface Processor (VIP), which are VIP-Distributed WRED and VIP-Distributed WFQ. These features can be used with CAR to deliver differentiated services.